1. Field of the Invention
A method utilized in a wireless communication and related communication device are disclosed, and more particularly, to a method of handling minimization of drive tests measurement in a wireless communication system and related communication device.
2. Description of the Prior Art
Coverage is something that a customer can easily notice through the terminal user interface (UI) (i.e. out-of-service area indication), and is a major criteria that a customer considers when comparing service provided by different operators. With the increase in data service provision, downlink throughput is also an important criterion by which many customers judge the performance of the network. Poor uplink coverage will impact user experience in terms of call setup failure/call drop/poor uplink voice quality.
Accordingly, it is very important for operators to be aware of the coverage/throughput their networks provide, and rigorous “drive tests” are performed to collect such information. However, what has to be taken account of is that the drive tests for network optimization purposes is costly and causes also additional CO2 emissions, so it is desirable to develop automated solutions, including involving UEs in the field, in 3GPP to reduce the operator costs for network deployment and operation. Therefore, minimization of drive tests (MDT) functionality involving measurement is performed by UE to collect information (or called measurement logs), to reduce network maintenance costs for operators, ensure faster optimization cycle resulting in higher customer satisfaction and nonetheless help to reduce the carbon emission to protect the environment.
Note that, for MDT, measurement configuration, measurement collection and reporting of the concerning measurement will always be done in cells of the same radio access technology (RAT) type. In addition, MDT measurement configuration is provided in a cell by dedicated control while the UE is in RRC connected state and implies that measurement configuration is valid in radio resource control (RRC) idle state, measurement configuration and logs are maintained when the UE is in the RRC idle state, and/or measurement configuration and logs are maintained when the UE is in that RAT. On the other hand, MDT measurement configuration and corresponding measurement logs are cleared by the UE at any public land mobile network (PLMN) change and switch off. The PLMN may rely on several RATs (e.g. Universal Mobile Telecommunications System (UMTS) and Long-Term Evolution (LTE)). An operator using UMTS or LTE can be identified by a PLMN code, which consists of a Mobile Network Code (MNC) and Mobile Country Code (MCC) pair.
However, the applicant notices that a UE may encounter validity problems associated to MDT measurement configuration and measurement logs as below based on a direct image on a basis of the prior art UMTS or LTE system.
In the first scenario, a UE with a MDT measurement configuration firstly registers to a PLMN, and then registers to another PLMN. According to the prior art, the UE clears the MDT measurement configuration and stops measurement log due to PLMN change. However, an operator may have more than one PLMN codes, e.g. with same MCC but with different MNCs. Therefore, the PLMN that the UE previously registers and currently registers may belong to the same operator. A behavior of invalidating or clearing MDT measurement configuration and logs results in that the network needs to configure MDT measurement configuration for the UE again and waits for the UE to collect measurement logs.
In the second scenario, a UE with MDT measurement configuration selects a closed subscriber group (CSG) cell, but is rejected due to that the UE is not authorized for this CSG. In this situation, UE does not have a registered PLMN (i.e. Registered PLMN changed to “No registered PLMN”), and may selects back to a micro cell in the previously registered PLMN. However, it is not clearly specified that whether the UE staying in the coverage of the previously registered PLMN shall clear the MDT measurement configuration. The behavior of validating or clearing MDT measurement configuration and logs results in that the network needs to configure MDT measurement configuration for the UE again and waits for the UE to collect measurement logs.
In the third scenario, a UE with MDT measurement configuration is rejected by a PLMN with a reject cause in a NAS message sent by the PLMN. The UE validates the MDT measurement configuration and corresponding measurement logs, and keeps measuring if the UE still camps on the PLMN. However, the PLMN considers that the UE is not valid and therefore does not retrieve measurement logs in the UE. This consumes UE power since the UE keeps measuring and consumes UE memory since the UE keeps logging.
In the fourth scenario, it is specified that all related MDT measurement configuration and logging shall be removed by the UE at switch off. However, the UE may perform a detach procedure instead of switch-off by entering a “flight mode” (where radio transmissions are not allowed). However, it is not clear whether the MDT measurement configuration is still valid after the UE enters a normal mode, i.e. performing an attach procedure again. The UE may perform MDT measurement and logging which is not wanted by the network. This unwanted MDT measurement and logging wastes battery power of the UE.